(1) Field of the Invention
The present invention relates to an electrode, which is for feeding an electrical power to a resistance heating layer, for use in an image forming apparatus and particularly in a fixing device.
(2) Description of the Related Art
An image forming apparatus such as a copy machine includes a fixing device for causing an unfixed image formed on a recording sheet to pass through a nip member formed by a heating rotary member and a pressurizing rotary member to fix the unfixed image onto the recording sheet. In recent years, in view points of energy saving and heating speed-up, there has been proposed a fixing method of using, as a heating rotary member, an endless belt including a resistance heating layer. This resistance heating layer is composed of a mixture of conductive materials, such as carbon powders and metallic powders, and heat-resistant insulating base materials, such as polyimide (PI) and a silicone rubber. An electrical power is fed to the resistance heating layer so as to directly heat the fixing belt to fix a toner image. According to this fixing method, a high heat efficiency is exhibited owing to a low heat capacity and a short distance from a heat source to a recording sheet that is to be heated. This enables short warm-up at a low electrical power consumption.
The heating method generally requires an electrical power feed to the resistance heating layer. Accordingly, the fixing device includes a power feeding member for feeding an electrical power to the resistance heating layer from the outside of the fixing belt, and also includes an electrode for receiving the electrical power fed from the power feeding member and transmitting the received electrical power to the resistance heating layer.
The above electrode is, for example, formed of a resin layer obtained by dispersing a conductive filler, or formed of adhered metal foil, metal mesh, and so on. These examples are disclosed in Japanese Patent Application Publication Nos. 2007-272223, 2009-109997, and 2009-92785.
However, in the case of use of an electrode formed of a resin layer obtained by dispersing a conductive filler, a higher electrical resistivity is exhibited compared with the case of use of an electrode formed of metal. Although this electrode does not need to generate heat, application of an electric current uselessly causes the electrode to generate heat. This results in a low heat efficiency.
On the other hand, in the case of use of an electrode formed of a metal having a low electrical resistivity, the mere use of metal for the electrode causes easy detachment of the electrode from a resistance heating layer.